Effect of Intraocular Pressure upon Electrical Excitability and Action Potentials of Human Retina

Abstract

Mechanical pressure of variable intensities was applied to the eyeball, to study its effect upon the electrical excitability of the human eye, and upon the ERG. The electrical excitability was measured with electrical phosphenes as an index.
1. The electrical excitability was lowered by 5, 25, 45 and 55 per cent under pressure of 50, 100, 200 and 300g., respectively in 15 seconds. The decrease caused by each pressure was not steadily progressive, but took place in two steps; the first decrease happened within 4 seconds and the second at 7 seconds from the onset of pressure.
2. It is known that the electrical excitability shows a temporary rise following an illumination. This effect of light was found to be abolished by pressure of about 200g.
3. The time taken for the electrical excitability to reach a maximum is different according to the wave-length of the light used for illumination. This color effect disappeared under pressure of about 200g.
4. In the experiments mentioned above, pressure was applied to a doughnut-shaped disc which was held in contact with the eyelids, the outer and the inner diameters of the disc being 25mm. and 18mm. respectively. Therefore it was necessary to compare the data obtained in this way with those obtained by other methods. Pressure values of 30 and 50g. in Bailliart's dynamometer were found to be equivalent to 130 and 230g. in our apparatus. The retinal arterial blood pressure was found 85g. with the dynamometer, and 480g. with our appratus.
5. ERGs of our subjects suffered from marked reduction under dynamometric pressure of 30g.
6. From these findings it was concluded that the observed decrease in the electrical excitability of the eye and especially the abolition of the color effect were due to local asphyxia caused by pressure.